Objects
in white (except the phaseless Moon) are outside
ten lunar distances (LD) at the date and time shown,
green objects are inside ten LD, yellow inside
Earth's gravitational sphere of influence (SOI), except the Sun, orange
inside two LD, and red inside one LD of Earth. Viewer location is at Earth's
center with the Sun directly to your back. Passing objects orbit the Sun and their motion is seen relative to
the Earth as it orbits the Sun. Object positions translated from a spherical sky dome to this rectangular chart
are increasingly distorted as they move north or south away from the celestial equator.
"Opposition longitude" (in degrees) is exactly opposite to the direction of the Sun through
Earth's center. Asteroids in this region, near the ecliptic and outside Earth's orbit, are at their brightest
as seen from Earth and thus most likely to be discovered and followed. Objects come and go, showing in the
viewer only while inside ten LD or under active observation (and leave trails only when inside 20 LD).
Viewer frame rate seems smoothest at the "good" speed setting, but your experience may differ.
Single-clicking anywhere on the skychart acts like hitting the [Run] button.
This Asteroid/Comet Connection (A/CC) animated illustration runs in HTML5 using data from
NASA/JPL Horizons (see credits) and the
Bright Star Catalog, with star colors per
Mitchell Charity. We welcome
feedback.

Side note to Web developers: This viewer is
the successor to a mostly complete Flash version (see screen shots
sans controls) created with Flex2 ActionScript. The project was finished by starting over again in HTML5 and
JavaScript, which required far less and far simpler coding. Data gathering and processing for this illustration
is all done with Python.

1. Ten lunar distances: One "lunar distance" (LD) is the average distance between Earth and Moon
(about 384,400 km., the same as 238,855 miles or 9.59 times around Earth's equator). Ten lunar
distances has no special astronomical importance but is a useful giant traveling "bubble" within which to organize
this special reporting. The approach of a small Solar-System body becomes more interesting when it nears or comes closer than 2.41 LD, as it encounters our planet's gravitational sphere of influence (SOI). Earth's gravity can change the orbits of objects passing through its SOI. The Moon also has its own SOI, which changes as its distance from Earth varies, but never extends much more than 0.18 LD. (The simple illustration above, with Earth and Moon not to scale, shows the Earth SOI as a dotted vertical blue line.) The "Earth-Moon system" is
generally defined as that region of space within a radius of one lunar distance from Earth, so an object can
pass quite close to the Moon yet not be described as coming "inside" the E-M system.

2. Data credit: All data on this page derived from orbit solutions comes from the NASA JPL
Solar System Dynamics (SSD) Group through its
Horizons system. All information about optical observations
comes from the IAU Minor Planet Center (MPC) and info
about radar observations comes from JPL SSD. The MPC, NASA, and JPL are not associated with this page or
A/CC, and responsibility for the interpretation of this information and its use here rests entirely with A/CC.
Important note: Approach times presented here as to-the-minute may have unstated uncertainties of a
few minutes, or many minutes or even hours for objects with old or very short observation spans, which is
significant because the Earth moves through its own diameter in about seven minutes. Thus actual encounter
distances may vary, occasionally by as much as ten lunar distances. See JPL's
Close Approach Tables for nominal vs. minimum
possible passage distances and times, and for their
note about uncertainties.

4. Skychart further notes: For illustrative purposes, the Sun and Moon are shown way out of
proportion to the background sky, each depicted as five degrees in apparent diameter instead of about a half
degree actual. All asteroids as viewed from Earth are single points of light without an apparent diameter.

5. Skychart known issues:

Please report problems. See here what the animated skychart should look like. If you are not getting something similar with JavaScript enabled in a modern HTML5-capable browser, please send a screen shot (in Windows, use [Alt]-[PrtScr] to copy to memory, open an image editor such as Windows Paint (found under Start/All Programs/Accessories), then paste and save as a JPEG).